Lithographic apparatus and device manufacturing method

ABSTRACT

An immersion lithography apparatus comprises a temperature controller configured to adjust a temperature of a projection system, a substrate and a liquid towards a common target temperature. Controlling the temperature of these elements and reducing temperature gradients may improve imaging consistency and general lithographic performance. Measures to control the temperature may include controlling the immersion liquid flow rate and liquid temperature, for example, via a feedback circuit.

This application is a continuation application of co-pending U.S. patentapplication Ser. No. 12/795,513, filed Jun. 7, 2010, which is acontinuation application of U.S. patent application Ser. No. 10/890,400,filed Jul. 14, 2004, now U.S. Pat. No. 7,738,074, which claims priorityfrom European patent application no. EP 03254466.0, filed Jul. 16, 2003,each of the foregoing applications incorporated herein in its entiretyby reference.

FIELD

The present invention relates to a lithographic apparatus and a methodfor manufacturing a device.

BACKGROUND

A lithographic apparatus is a machine that applies a desired patternonto a substrate, usually onto a target portion of the substrate. Alithographic apparatus can be used, for example, in the manufacture ofintegrated circuits (ICs). In that instance, a patterning device, whichis alternatively referred to as a mask or a reticle, may be used togenerate a circuit pattern to be formed on an individual layer of theIC. This pattern can be transferred onto a target portion (e.g.comprising part of, one, or several dies) on a substrate (e.g. a siliconwafer). Transfer of the pattern is typically via imaging onto a layer ofradiation-sensitive material (resist) provided on the substrate. Ingeneral, a single substrate will contain a network of adjacent targetportions that are successively patterned. Known lithographic apparatusinclude so-called steppers, in which each target portion is irradiatedby exposing an entire pattern onto the target portion at one time, andso-called scanners, in which each target portion is irradiated byscanning the pattern through a radiation beam in a given direction (the“scanning”-direction) while synchronously scanning the substrateparallel or anti-parallel to this direction. It is also possible totransfer the pattern from the patterning device to the substrate byimprinting the pattern onto the substrate.

It has been proposed to immerse the substrate in the lithographicprojection apparatus in a liquid having a relatively high refractiveindex, e.g. water, so as to fill a space between the final element ofthe projection system and the substrate. The point of this is to enableimaging of smaller features since the exposure radiation will have ashorter wavelength in the liquid. (The effect of the liquid may also beregarded as increasing the effective NA of the system and alsoincreasing the depth of focus.) Other immersion liquids have beenproposed, including water with solid particles (e.g. quartz) suspendedtherein.

However, submersing the substrate or substrate and substrate table in abath of liquid (see, for example, U.S. Pat. No. 4,509,852, herebyincorporated in its entirety by reference) means that there is a largebody of liquid that must be accelerated during a scanning exposure. Thisrequires additional or more powerful motors and turbulence in the liquidmay lead to undesirable and unpredictable effects.

One of the solutions proposed is for a liquid supply system to provideliquid on only a localized area of the substrate and in between thefinal element of the projection system and the substrate (the substrategenerally has a larger surface area than the final element of theprojection system). One way which has been proposed to arrange for thisis disclosed in PCT patent application WO 99/49504, hereby incorporatedin its entirety by reference. As illustrated in FIGS. 2 and 3, liquid issupplied by at least one inlet IN onto the substrate, preferably alongthe direction of movement of the substrate relative to the finalelement, and is removed by at least one outlet OUT after having passedunder the projection system. That is, as the substrate is scannedbeneath the element in a −X direction, liquid is supplied at the +X sideof the element and taken up at the −X side. FIG. 2 shows the arrangementschematically in which liquid is supplied via inlet IN and is taken upon the other side of the element by outlet OUT which is connected to alow pressure source. In the illustration of FIG. 2 the liquid issupplied along the direction of movement of the substrate relative tothe final element, though this does not need to be the case. Variousorientations and numbers of in- and out-lets positioned around the finalelement are possible, one example is illustrated in FIG. 3 in which foursets of an inlet with an outlet on either side are provided in a regularpattern around the final element.

It is typically important to reduce or minimize temperature variationsin components that influence the path of imaging radiation. Thermalexpansion and contraction of optical components such as lenses andmirrors may lead to distortions of the image reaching the substrate asmay temperature induced variations in the refractive index of animmersion liquid in an immersion lithographic apparatus. Control ofcomponent temperatures is normally possible by limiting the extent andproximity of dissipative processes, both electrical and mechanical, orof any other heat flux sources (i.e. sources that provide or absorbheat), and ensuring good thermal connection between components and highheat capacity elements. However, despite employing measures such asthese with regard to optical elements, image distortions traceable tovariations in temperature and/or in local beam intensity continue to bedetected.

SUMMARY

Accordingly, it would be advantageous, for example, to reduce imagedistortion due to temperature gradients in the substrate and immersionliquid.

According to an aspect of the invention, there is provided alithographic apparatus comprising:

an illumination system configured to condition a radiation beam;

a support constructed to hold a patterning device, the patterning devicebeing capable of imparting the radiation beam with a pattern in itscross-section to form a patterned radiation beam;

a substrate table constructed to hold a substrate;

a projection system configured to project the patterned radiation beamonto a target portion of the substrate; and

a liquid supply system configured to at least partly fill a spacebetween the projection system and the substrate with a liquid, theliquid supply system comprising a temperature controller configured toadjust the temperature of the substrate, the liquid and at least a partof the projection system towards a substantially common targettemperature.

According to a further aspect of the invention, there is provided alithographic apparatus comprising:

an illumination system configured to condition a radiation beam;

a support constructed to hold a patterning device, the patterning devicebeing capable of imparting the radiation beam with a pattern in itscross-section to form a patterned radiation beam;

a substrate table constructed to hold a substrate;

a projection system configured to project the patterned radiation beamonto a target portion of the substrate;

a liquid supply system configured to at least partly fill a spacebetween the projection system and the substrate with a liquid; and

a projection system compensator configured to adjust an optical propertyof the projection system in response to a distortion in a patternexposed on the substrate caused by a difference in temperature of theprojection system, the substrate, the liquid, or any combinationthereof, from a target temperature.

According to a further aspect of the invention, there is provided adevice manufacturing method comprising:

projecting, using a projection system of a lithographic apparatus, apatterned beam of radiation through a liquid onto a target portion of asubstrate; and

adjusting the temperature of the substrate, the liquid and at least apart of the projection system towards a substantially common targettemperature.

According to a further aspect of the invention, there is provided adevice manufacturing method comprising:

projecting, using a projection system of a lithographic apparatus, apatterned beam of radiation through a liquid onto a target portion of asubstrate; and

adjusting an optical property of the projection system in response to adistortion in a pattern exposed on the substrate caused by a differencein temperature of the projection system, the substrate, the liquid, orany combination thereof, from a target temperature.

Although specific reference may be made in this text to the use of theapparatus according to the invention in the manufacture of ICs, itshould be explicitly understood that such an apparatus has many otherpossible applications. For example, it may be employed in themanufacture of integrated optical systems, guidance and detectionpatterns for magnetic domain memories, liquid-crystal display panels,thin-film magnetic heads, etc. The skilled artisan will appreciate that,in the context of such alternative applications, any use of the terms“reticle”, “wafer” or “die” in this text should be considered as beingreplaced by the more general terms “mask”, “substrate” and “targetportion”, respectively.

In the present document, the terms “radiation” and “beam” are used toencompass all types of electromagnetic radiation, including ultravioletradiation (e.g. with a wavelength of 365, 248, 193, 157 or 126 nm).

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich:

FIG. 1 depicts a lithographic apparatus according to an embodiment ofthe invention;

FIGS. 2 and 3 depict a liquid supply system for use in a lithographicprojection apparatus;

FIG. 4 depicts another liquid supply system for use in a lithographicprojection apparatus;

FIG. 5 depicts a liquid supply system and seal member according to anembodiment of the invention;

FIG. 6 depicts a flow rate adjustment device and liquid temperatureadjustment device according to an embodiment of the invention; and

FIG. 7 depicts a lithographic apparatus according to an embodiment ofthe invention, comprising a projection system compensator, patternedradiation beam distortion detector, temperature sensor and storagedevice.

DETAILED DESCRIPTION

FIG. 1 schematically depicts a lithographic apparatus according to oneembodiment of the invention. The apparatus comprises:

an illumination system (illuminator) IL configured to condition aradiation beam PB (e.g. UV radiation or DUV radiation);

a support structure (e.g. a mask table) MT constructed to support apatterning device (e.g. a mask) MA and connected to a first positionerPM configured to accurately position the patterning device in accordancewith certain parameters;

a substrate table (e.g. a wafer table) WT constructed to hold asubstrate (e.g. a resist-coated wafer) W and connected to a secondpositioner PW configured to accurately position the substrate inaccordance with certain parameters; and

a projection system (e.g. a refractive projection lens system) PLconfigured to project a pattern imparted to the radiation beam PB bypatterning device MA onto a target portion C (e.g. comprising one ormore dies) of the substrate W.

The illumination system may include various types of optical components,such as refractive, reflective, magnetic, electromagnetic, electrostaticor other types of optical components, or any combination thereof, fordirecting, shaping, or controlling radiation.

The support structure supports, i.e. bears the weight of, the patterningdevice. It holds the patterning device in a manner that depends on theorientation of the patterning device, the design of the lithographicapparatus, and other conditions, such as for example whether or not thepatterning device is held in a vacuum environment. The support structurecan use mechanical, vacuum, electrostatic or other clamping techniquesto hold the patterning device. The support structure may be a frame or atable, for example, which may be fixed or movable as required. Thesupport structure may ensure that the patterning device is at a desiredposition, for example with respect to the projection system. Any use ofthe terms “reticle” or “mask” herein may be considered synonymous withthe more general term “patterning device.”

The term “patterning device” used herein should be broadly interpretedas referring to any device that can be used to impart a radiation beamwith a pattern in its cross-section such as to create a pattern in atarget portion of the substrate. It should be noted that the patternimparted to the radiation beam may not exactly correspond to the desiredpattern in the target portion of the substrate, for example if thepattern includes phase-shifting features or so called assist features.Generally, the pattern imparted to the radiation beam will correspond toa particular functional layer in a device being created in the targetportion, such as an integrated circuit.

The patterning device may be transmissive or reflective. Examples ofpatterning devices include masks, programmable mirror arrays, andprogrammable LCD panels. Masks are well known in lithography, andinclude mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. An exampleof a programmable mirror array employs a matrix arrangement of smallmirrors, each of which can be individually tilted so as to reflect anincoming radiation beam in different directions. The tilted mirrorsimpart a pattern in a radiation beam which is reflected by the mirrormatrix.

The term “projection system” used herein should be broadly interpretedas encompassing any type of projection system, including refractive,reflective, catadioptric, magnetic, electromagnetic and electrostaticoptical systems, or any combination thereof, as appropriate for theexposure radiation being used, or for other factors such as the use ofan immersion liquid or the use of a vacuum. Any use of the term“projection lens” herein may be considered as synonymous with the moregeneral term “projection system”.

As here depicted, the apparatus is of a transmissive type (e.g.employing a transmissive mask). Alternatively, the apparatus may be of areflective type (e.g. employing a programmable mirror array of a type asreferred to above, or employing a reflective mask).

The lithographic apparatus may be of a type having two (dual stage) ormore substrate tables (and/or two or more mask tables). In such“multiple stage” machines the additional tables may be used in parallel,or preparatory steps may be carried out on one or more tables while oneor more other tables are being used for exposure.

Referring to FIG. 1, the illuminator IL receives a radiation beam from aradiation source SO. The source and the lithographic apparatus may beseparate entities, for example when the source is an excimer laser. Insuch cases, the source is not considered to form part of thelithographic apparatus and the radiation beam is passed from the sourceSO to the illuminator IL with the aid of a beam delivery system BDcomprising, for example, suitable directing mirrors and/or a beamexpander. In other cases the source may be an integral part of thelithographic apparatus, for example when the source is a mercury lamp.The source SO and the illuminator IL, together with the beam deliverysystem BD if required, may be referred to as a radiation system.

The illuminator IL may comprise an adjuster AD for adjusting the angularintensity distribution of the radiation beam. Generally, at least theouter and/or inner radial extent (commonly referred to as σ-outer andσ-inner, respectively) of the intensity distribution in a pupil plane ofthe illuminator can be adjusted. In addition, the illuminator IL maycomprise various other components, such as an integrator IN and acondenser CO. The illuminator may be used to condition the radiationbeam, to have a desired uniformity and intensity distribution in itscross-section.

The radiation beam PB is incident on the patterning device (e.g., maskMA), which is held on the support structure (e.g., mask table MT), andis patterned by the patterning device. Having traversed the mask MA, theradiation beam PB passes through the projection system PL, which focusesthe beam onto a target portion C of the substrate W. With the aid of thesecond positioner PW and position sensor IF (e.g. an interferometricdevice, linear encoder or capacitive sensor), the substrate table WT canbe moved accurately, e.g. so as to position different target portions Cin the path of the radiation beam PB. Similarly, the first positioner PMand another position sensor (which is not explicitly depicted in FIG. 1)can be used to accurately position the mask MA with respect to the pathof the radiation beam PB, e.g. after mechanical retrieval from a masklibrary, or during a scan. In general, movement of the mask table MT maybe realized with the aid of a long-stroke module (coarse positioning)and a short-stroke module (fine positioning), which form part of thefirst positioner PM. Similarly, movement of the substrate table WT maybe realized using a long-stroke module and a short-stroke module, whichform part of the second positioner PW. In the case of a stepper (asopposed to a scanner) the mask table MT may be connected to ashort-stroke actuator only, or may be fixed. Mask MA and substrate W maybe aligned using mask alignment marks M1, M2 and substrate alignmentmarks P1, P2. Although the substrate alignment marks as illustratedoccupy dedicated target portions, they may be located in spaces betweentarget portions (these are known as scribe-lane alignment marks).Similarly, in situations in which more than one die is provided on themask MA, the mask alignment marks may be located between the dies.

The depicted apparatus could be used in at least one of the followingmodes:

1. In step mode, the mask table MT and the substrate table WT are keptessentially stationary, while an entire pattern imparted to theradiation beam is projected onto a target portion C at one time (i.e. asingle static exposure). The substrate table WT is then shifted in the Xand/or Y direction so that a different target portion C can be exposed.In step mode, the maximum size of the exposure field limits the size ofthe target portion C imaged in a single static exposure.

2. In scan mode, the mask table MT and the substrate table WT arescanned synchronously while a pattern imparted to the radiation beam isprojected onto a target portion C (i.e. a single dynamic exposure). Thevelocity and direction of the substrate table WT relative to the masktable MT may be determined by the (de-)magnification and image reversalcharacteristics of the projection system PL. In scan mode, the maximumsize of the exposure field limits the width (in the non-scanningdirection) of the target portion in a single dynamic exposure, whereasthe length of the scanning motion determines the height (in the scanningdirection) of the target portion.

3. In another mode, the mask table MT is kept essentially stationaryholding a programmable patterning device, and the substrate table WT ismoved or scanned while a pattern imparted to the radiation beam isprojected onto a target portion C. In this mode, generally a pulsedradiation source is employed and the programmable patterning device isupdated as required after each movement of the substrate table WT or inbetween successive radiation pulses during a scan. This mode ofoperation can be readily applied to maskless lithography that utilizesprogrammable patterning device, such as a programmable mirror array of atype as referred to above.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

FIGS. 5 and 6 show a liquid supply system 10 and features 21, 22 and 23of the temperature controller according to an embodiment of theinvention. The projection system PL, substrate W and immersion liquidmay have temperature dependent properties that may influence the qualityof the image projected to the substrate W. Heat flux from varioussources may lead to temperature offsets in one or more of these elementsand even to temperature gradients if no counter-measures are employed.This possibility may be exacerbated by the relatively low thermalconductance and heat capacity of the substrate (due both to the materialused and the thin geometry). Temperature gradients may lead to thermalexpansion/contraction gradients that, depending on the element inquestion may distort the projected image. This may be a particularlydifficult problem when the temperature profile changes as the imagingbeam moves relative to the substrate W, as may occur in the substrateitself, for example. In the case of the immersion liquid, localizedhotspots or cold spots on the substrate W may also lead to temperaturegradients in the liquid, with liquid located close to the hotspots/coldspots being higher/lower in temperature than liquid located furtheraway. Since the refractive index is generally temperature dependent,this may influence the path the imaging radiation takes through theliquid and will distort the image. By using a temperature controllerthat ensures not only the constancy of the projection system temperaturebut also that of the substrate W and immersion liquid, distortion of theimage due to these factors may be reduced.

In the embodiment shown, the liquid supply system 10 supplies liquid toan imaging-field reservoir 12 between the projection system PL and thesubstrate W. The liquid is, in an embodiment, chosen to have arefractive index substantially greater than 1 meaning that thewavelength of the projection beam is shorter in the liquid than in airor a vacuum, allowing smaller features to be resolved. It is well knownthat the resolution of a projection system is determined, inter alia, bythe wavelength of the projection beam and the numerical aperture of thesystem. The presence of the liquid may also be regarded as increasingthe effective numerical aperture.

The reservoir 12 is bounded at least in part by a seal member 13positioned below and surrounding the final element of the projectionsystem PL. The seal member 13 extends a little above the final elementof the projection system PL and the liquid level rises above the bottomend of the final element of the projection system PL. The seal member 13has an inner periphery that at the upper end closely conforms to thestep of the projection system or the final element thereof and may,e.g., be round. At the bottom, the inner periphery closely conforms tothe shape of the image field, e.g. rectangular but may be any shape.

Between the seal member 13 and the substrate W, the liquid may beconfined to the reservoir by a contact-less seal 14, such as a gas sealformed by gas provided under pressure to the gap between the seal member13 and the substrate W.

As has been discussed above, lithographic apparatuses may be extremelysensitive to thermally induced changes to the physical properties ofoptical elements. These changes may include thermalexpansion/contraction or changes in intrinsic properties such asrefractive index. In an apparatus as complex as a typical lithographyapparatus, there will inevitably be a number of important heat fluxsources that may contribute to temperature variations in critical areas.These sources may derive from dissipation arising in electrically drivendevices, with or without moving parts, from variations in the externalenvironment temperature, and/or from evaporation/condensation of fluids.An important source of heat stems from the absorption of imagingradiation by the substrate W (leading to overlay errors). This sourcemay also heat the substrate table holding the substrate W and theimmersion liquid via convection from the substrate. Bulk temperatureincreases may arise via this mechanism particularly for shorterwavelength radiation, such as 157 nm. Care may be taken to minimizeheating caused within the apparatus and to prevent excessive variationsin the external environment temperature but it is difficult tocompletely eradicate their effects particularly where dissipativeheating occurs within the optical system itself.

These temperature variations may be relatively homogeneous leading touniform changes in the image reaching the substrate W (such as uniformtranslation or magnification/shrinkage) or they may includecontributions with a stronger spatial dependence. These lattervariations may be considered more damaging because they may distort theimage in a non-uniform way. The substrate W, for example, may beparticularly vulnerable to such temperature variations since it isheated locally by the imaging radiation. In immersion lithographysystems, the immersion liquid may also lead to temperature dependentoptical properties because the refractive index of the liquid may varywith temperature.

Thermal management of these components is not amenable to the samemethods used for standard optical elements. In the case of the substrateW, several factors are important. To begin with, the plate-like geometryof the substrate W suffers in two respects: firstly, each portion of thesubstrate W is in relatively poor thermal contact with the rest of thesubstrate W, so that heat disperses slowly, and secondly, the heatcapacity of the substrate W per unit area will be reduced relative to athicker slab. Both of these factors mean that a smaller amount of energyfrom the imaging radiation or other heat flux source may be necessary tolocally heat or cool the substrate W to a given temperature.Furthermore, these problems may be compounded by the fact that strictalignment tolerances and the required mobility of the substrate Wgreatly restrict the deployment of mechanical thermal connections to thesubstrate W. In the case of the immersion liquid, heat exchanged betweenthe substrate W and the liquid tends to heat or cool the liquid in anon-uniform way by convective currents and the like stimulated bytemperature induced density variations rather than by conduction. Withina stationary liquid, this process may happen slowly leading tosubstantial temperature (and thus refractive index) gradients within theliquid. The contact area between the liquid and the substrate isrelatively large so that heat may be exchanged efficiently between thetwo.

In the embodiments depicted in FIGS. 5 and 6, the immersion liquidexchanges heat with the final element of the projection system PL andthe substrate W. In order to carry the heated or cooled liquid away, theliquid is made to flow (see arrows 11) through the imaging-fieldreservoir 12. Convection typically tends to take place within a thinlayer (approximately 300 μm) near the heated or cooled element incontact with the liquid, due to the effects of laminar flow. Moreeffective heat exchange may be obtained by directing the flow towardsthe heated or cooled element in question (i.e. towards the substrate Win the embodiment shown in FIG. 5). Particularly in the case where thetemperature of the substrate W is of concern, it may be advantageous toposition the immersion liquid outlet underneath the seal member 13 (asshown) and directed towards the substrate W. This arrangement may helpto ensure relatively fresh immersion liquid near to the substrate W andminimize or reduce the influx of excessively heated or cooled liquidthat may be dragged into the imaging-field reservoir 12 at its lowerboundaries (where the seal member 13 meets the substrate W).

Increasing the flow rate may also improve the heat exchange between theliquid and elements with which it is in contact. In order to exploitthis fact, the temperature controller may comprise a liquid flow rateadjustment device 21, the liquid flow rate being adjusted so as tooptimize a difference between a common target temperature and thetemperatures of the final element of the projection system PL, thesubstrate W and the liquid. Heat exchange with the liquid causes thetemperatures of the final element of the projection system and thesubstrate to tend towards the temperature of the liquid. Increasing theflow rate of liquid over these elements increases the efficiency of thisprocess. However, there may be a limit to how high the flow rate canreach without itself degrading imaging performance via turbulence orfrictional heating. The flow rate controlling process may be carried outby varying the power of a pumping device, used to circulate theimmersion liquid, or by changing the flow impedance of the liquid supplysystem 10 (by changing the cross-section of circulation channels formingpart thereof, for example).

The temperature controller may also comprise a liquid temperatureadjustment device 22, the temperature of the liquid flowing in theliquid supply system 10 being adjusted so as to optimize a differencebetween a common target temperature and the temperatures of the finalelement of the projection system PL, the substrate W and the liquid.Adjusting the temperature of the immersion liquid may be carried outinside a temperature adjustment reservoir 24, within which thetemperature adjustment device 22 may be immersed along with thermometry25. The temperature adjustment device 22 may act to cool the liquid, viaa refrigeration device, towards the common target temperature or belowto compensate for heating of the liquid elsewhere in the liquid supplysystem 10. Alternatively, the temperature adjustment device 22 may actto heat the liquid, for example by means of an electrical heater,towards the common target temperature or above. The action of thetemperature adjustment device 22 may be realized by a liquid-to-liquidheat exchanger with a first input being to the immersion liquid and asecond input to a supply of temperature controlled water. An advantageof this arrangement is that a supply of temperature controlled water mayalready be available from arrangements to service other parts of thelithographic apparatus. The projection system PL, for example, mayalready be cooled by a continuous flow of such water. Additionally, thetemperature controlled water does not need to be chemically purifiedbecause it is re-circulated.

The temperature controller may comprise a PID(Proportional-Integral-Differential) controller 23, a type of feedbackcontroller, for achieving efficient convergence towards the commontarget temperature. The PID controller 23 may, for example, be arrangedto ensure efficient convergence of one of more of the temperatures ofthe final element of the projection system, the substrate W and theliquid with the common target temperature (i.e. as quickly as possibleand without overshoot).

The PID controller 23 controls the operation of the flow rate adjustmentdevice 21 and/or the liquid temperature adjustment device 22, taking asinput the temperature profile of the final element of the projectionsystem T1 (in an embodiment, measured at a plurality of locations), thetemperature profile of the substrate and substrate table T2 (in anembodiment, measured at a plurality of locations), the temperatureprofile of the liquid T3 (in an embodiment, measured at a plurality oflocations), and the common target temperature T4. The operation of thePID controller 23 is not limited to the above context and may be used toregulate cooling processes throughout the lithographic apparatus.

The common target temperature may be set to a predetermined value. Thepredetermined value may be determined by the temperature at which theprojection system has been calibrated.

It has been described above how temperature variations in opticallycritical components, such as the final element of the projection systemPL, the substrate W and the immersion liquid, can damage the imagingproperties of the lithographic apparatus. FIG. 7 depicts an embodimentin which radiation beam distortions arising in this way are compensatedusing a projection system compensator 28, which is configured to adjustthe optical properties of the projection system PL in response to adistortion in the pattern generated on the substrate W caused by adifference in temperature of at least one of the final element of theprojection system PL, the substrate W and the liquid from a targettemperature (such as a temperature at which the system has beencalibrated). The distortion in the pattern generated on the substrate Wmay be caused either by a distortion in the patterned radiation beam,caused for example by variations in the temperature of the immersionliquid and/or final element of the projection system PL from the targettemperature, or by temperature induced distortions of the substrateduring exposure by the patterned radiation beam (which may or may not bedistorted) or distortions in the pattern generated on the substrate Woccurring in this case when the distorted substrate regains its normalform.

The projection system compensator 28 can adjust the imaging propertiesof the projection system PL via one or more adjustable elements arrangedtherein (such as actuatable lenses or moveable mirrors). The effect thatthese adjustments will have on the form of the patterned radiation beamwill be calibrated beforehand. This may be achieved by actuating eachadjustable element over its operating range and analyzing the form ofthe patterned radiation beam that emerges. Generally speaking, aradiation beam distortion can be expressed as an expansion infundamental distortion modes (such as those expressed by a Zernikeseries, for example). A calibration table may comprise matricesconsisting of coefficients in such an expansion and settings for eachadjustable element. If the adjustable elements are chosen to coveradequately the main types of distortion, their use in concert shouldenable compensation of most types of distortion that are likely to occurfrom temperature variations in the immersion liquid and the elementssurrounding it.

The projection system compensator 28 may receive input from a patternedradiation beam distortion detector 30, which in the example embodimentillustrated is linked to an optical detector 36 within the projectionsystem PL but alternative devices may also be provided for this purpose.The optical detector 36 here is arranged to capture stray light 38 fromthe main patterned radiation beam that reflects from the substrate. Thisstray light may be analyzed to determine the patterned beam distortionby the patterned beam distortion detector 30. This may be achieved, forexample, by means of a comparator, which compares the detected radiationwith a standard pattern that was obtained under control conditions. Theextent of deviation from the standard pattern can be analyzed tocharacterize distortion of the patterned beam. This approach has theadvantage of being a direct measure of temperature induced distortions.It is also applicable in-situ during normal operation of thelithographic apparatus and as such enables the projection systemcompensator to work dynamically in real time.

An alternative or additional approach is to measure the temperatureprofile of the elements likely to cause distortion of the patternedradiation beam and determine from calibration measurements orcalculation what the resulting distortion is likely to be. Theprojection system compensator 28 may then compensate the projectionsystem PL as described above without directly measuring the distortionitself. FIG. 7 shows schematic arrangements of components 32 a, 32 b and32 c of a temperature sensor. These components 32 a, 32 b and 32 c aredepicted as layers and may, for example, each comprise one or aplurality of thermometers, which may be arranged to determine thetemperature of at least a part of the final element of the projectionsystem PL, the substrate W (and/or substrate table WT), the liquid, orany combination thereof. Each of the components 32 a, 32 b and 32 c arecapable of communicating with the projection system compensator 28 viadata transmission lines 34 a, 34 b and 34 c. The amount of adjustment toapply to each of the adjustable elements of the projection system PLrequires reference in this case to a second calibration table, which isstored in a storage device 40. In this case, the calibration data storesinformation derived from previous measurements recording therelationship between a given element temperature or temperature profileand the resulting distortion. Once the predicted distortion isestablished, the projection system compensator can operate as it wouldhad the distortion information been forwarded from the patternedradiation beam distortion detector 28.

The process thus described may be carried out in real time to adaptdynamically to unexpected and/or uncontrollable temperature variationsin the region around the imaging-field reservoir 12. As depicted, theprojection system compensator 28 and the patterned radiation beamdistortion detection device 30 may form a feedback loop, which may bearranged to keep radiation beam distortion within certain predefinedlimits. A PID controller similar to that employed to control theimmersion liquid temperature may be incorporated to ensure stability andefficient convergence.

In an embodiment, the above arrangements have an advantage of being ableto respond quickly to small variations in the temperature of criticalelements. The system may usefully be used in combination with systemsthat minimize temperature variations themselves to achieve a high degreeof temperature stability and imaging accuracy.

In an embodiment, there is provided a lithographic apparatus comprising:an illumination system configured to condition a radiation beam; asupport constructed to hold a patterning device, the patterning devicebeing capable of imparting the radiation beam with a pattern in itscross-section to form a patterned radiation beam; a substrate tableconstructed to hold a substrate; a projection system configured toproject the patterned radiation beam onto a target portion of thesubstrate; and a liquid supply system configured to at least partly filla space between the projection system and the substrate with a liquid,the liquid supply system comprising a temperature controller configuredto adjust the temperature of the substrate, the liquid and at least apart of the projection system towards a substantially common targettemperature.

In an embodiment, the temperature controller comprises a liquid flowrate adjustment device configured to adjust a flow rate of the liquid soas to optimize a difference between the substantially common targettemperature and the temperatures of the substrate, the liquid and the atleast part of the projection system. In an embodiment, the temperaturecontroller comprises a liquid temperature adjustment device configuredto adjust the liquid temperature so as to optimize a difference betweenthe substantially common target temperature and the temperatures of thesubstrate, the liquid and the at least part of the projection system. Inan embodiment, the temperature controller comprises a PID controllerconfigured to achieve convergence towards the substantially commontarget temperature. In an embodiment, the substantially common targettemperature is set to a predetermined value.

In an embodiment, there is provided a lithographic apparatus comprising:an illumination system configured to condition a radiation beam; asupport constructed to hold a patterning device, the patterning devicebeing capable of imparting the radiation beam with a pattern in itscross-section to form a patterned radiation beam; a substrate tableconstructed to hold a substrate; a projection system configured toproject the patterned radiation beam onto a target portion of thesubstrate; a liquid supply system configured to at least partly fill aspace between the projection system and the substrate with a liquid; anda projection system compensator configured to adjust an optical propertyof the projection system in response to a distortion in a patternexposed on the substrate caused by a difference in temperature of theprojection system, the substrate, the liquid, or any combinationthereof, from a target temperature.

In an embodiment, the projection system compensator comprises apatterned radiation beam distortion detector arranged to detectdistortion of the patterned radiation beam. In an embodiment, thepatterned radiation beam distortion detector comprises: an opticaldetector arranged to detect radiation of the patterned radiation beamreflected from the substrate; and a comparator configured to compare thedetected radiation with a standard pattern in order to detect adistortion of the patterned radiation beam. In an embodiment, theprojection system compensator comprises: a temperature sensor arrangedto measure the temperature of at least a part of the projection system,the substrate, the liquid, or any combination thereof; and a storagedevice capable of storing a table of calibration data, the calibrationdata representing adjustments to be applied to an optical property ofthe projection system in response to a measurement of the temperaturesensor. In an embodiment, the projection system compensator comprises aPID controller configured to achieve convergence of the distortion towithin a limit.

In an embodiment, there is provided a device manufacturing methodcomprising: projecting, using a projection system of a lithographicapparatus, a patterned beam of radiation through a liquid onto a targetportion of a substrate; and adjusting the temperature of the substrate,the liquid and at least a part of the projection system towards asubstantially common target temperature.

In an embodiment, adjusting the temperature comprises adjusting a flowrate of the liquid so as to optimize a difference between thesubstantially common target temperature and the temperatures of thesubstrate, the liquid and the at least part of the projection system. Inan embodiment, adjusting the temperature comprises adjusting the liquidtemperature so as to optimize a difference between the substantiallycommon target temperature and the temperatures of the substrate, theliquid and the at least part of the projection system. In an embodiment,adjusting the temperature is performed using a PID controller to achieveconvergence towards the substantially common target temperature. In anembodiment, the substantially common target temperature is set to apredetermined value.

In an embodiment, there is provided a device manufacturing methodcomprising: projecting, using a projection system of a lithographicapparatus, a patterned beam of radiation through a liquid onto a targetportion of a substrate; and adjusting an optical property of theprojection system in response to a distortion in a pattern exposed onthe substrate caused by a difference in temperature of the projectionsystem, the substrate, the liquid, or any combination thereof, from atarget temperature.

In an embodiment, the method comprises detecting distortion of thepatterned radiation beam. In an embodiment, detecting distortion of thepatterned radiation beam comprises detecting radiation of the patternedradiation beam reflected from the substrate and comparing the detectedradiation with a standard pattern in order to detect a distortion of thepatterned radiation beam. In an embodiment, the method comprisesmeasuring the temperature of at least a part of the projection system,the substrate, the liquid, or any combination thereof and whereinadjusting an optical property comprises determining the adjustment to beapplied to an optical property of projection system from a table ofcalibration data using the measurement from the temperature sensor. Inan embodiment, adjusting an optical property is performed using a PIDcontroller to achieve convergence of the distortion to within a limit.

Another liquid supply system which has been proposed is to provide theliquid supply system with a seal member which extends along at least apart of a boundary of the space between the final element of theprojection system and the substrate table. The seal member issubstantially stationary relative to the projection system in the XYplane though there may be some relative movement in the Z direction (inthe direction of the optical axis). A seal is formed between the sealmember and the surface of the substrate. In an embodiment, the seal is acontactless seal such as a gas seal. Such a system with a gas seal isdisclosed in U.S. patent application U.S. Ser. No. 10/705,783, herebyincorporated in its entirety by reference.

A further immersion lithography solution with a localized liquid supplysystem is shown in FIG. 4. Liquid is supplied by two groove inlets IN oneither side of the projection system PL and is removed by a plurality ofdiscrete outlets OUT arranged radially outwardly of the inlets IN. Theinlets IN and OUT can be arranged in a plate with a hole in its centerand through which the projection beam is projected. Liquid is suppliedby one groove inlet IN on one side of the projection system PL andremoved by a plurality of discrete outlets OUT on the other side of theprojection system PL, causing a flow of a thin film of liquid betweenthe projection system PL and the substrate W. The choice of whichcombination of inlet IN and outlets OUT to use can depend on thedirection of movement of the substrate W (the other combination of inletIN and outlets OUT being inactive).

In European Patent Application No. 03257072.3, the idea of a twin ordual stage immersion lithography apparatus is disclosed. Such anapparatus is provided with two tables for supporting a substrate.Leveling measurements are carried out with a table at a first position,without immersion liquid, and exposure is carried out with a table at asecond position, where immersion liquid is present. Alternatively, theapparatus has only one table.

The present invention can be applied to any immersion lithographyapparatus, in particular, but not exclusively, those liquid supplysystems mentioned above.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,flat-panel displays, liquid-crystal displays (LCDs), thin-film magneticheads, etc. The skilled artisan will appreciate that, in the context ofsuch alternative applications, any use of the terms “wafer” or “die”herein may be considered as synonymous with the more general terms“substrate” or “target portion”, respectively. The substrate referred toherein may be processed, before or after exposure, in for example atrack (a tool that typically applies a layer of resist to a substrateand develops the exposed resist), a metrology tool and/or an inspectiontool. Where applicable, the disclosure herein may be applied to such andother substrate processing tools. Further, the substrate may beprocessed more than once, for example in order to create a multi-layerIC, so that the term substrate used herein may also refer to a substratethat already contains multiple processed layers.

Although specific reference may have been made above to the use ofembodiments of the invention in the context of optical lithography, itwill be appreciated that the invention may be used in otherapplications, for example imprint lithography, and where the contextallows, is not limited to optical lithography. In imprint lithography atopography in a patterning device defines the pattern created on asubstrate. The topography of the patterning device may be pressed into alayer of resist supplied to the substrate whereupon the resist is curedby applying electromagnetic radiation, heat, pressure or a combinationthereof. The patterning device is moved out of the resist leaving apattern in it after the resist is cured.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.having a wavelength of or about 365, 248, 193, 157 or 126 nm) andextreme ultra-violet (EUV) radiation (e.g. having a wavelength in therange of 5-20 nm), as well as particle beams, such as ion beams orelectron beams.

The term “lens”, where the context allows, may refer to any one orcombination of various types of optical components, includingrefractive, reflective, magnetic, electromagnetic and electrostaticoptical components.

While specific embodiments of the invention have been described above,it will be appreciated that the invention may be practiced otherwisethan as described. For example, the invention may take the form of acomputer program containing one or more sequences of machine-readableinstructions describing a method as disclosed above, or a data storagemedium (e.g. semiconductor memory, magnetic or optical disk) having sucha computer program stored therein.

The descriptions above are intended to be illustrative, not limiting.Thus, it will be apparent to one skilled in the art that modificationsmay be made to the invention as described without departing from thescope of the claims set out below.

1. A lithographic apparatus comprising: an illumination systemconfigured to condition a radiation beam; a support constructed to holda patterning device, the patterning device being capable of impartingthe radiation beam with a pattern in its cross-section to form apatterned radiation beam; a substrate table constructed to hold asubstrate; a projection system configured to project the patternedradiation beam onto a target portion of the substrate; and a liquidsupply system configured to at least partly fill a space between theprojection system and the substrate with a liquid, the liquid supplysystem comprising a temperature controller configured to adjust thetemperature of the substrate, the liquid and at least a part of theprojection system towards a substantially common target temperature. 2.The lithographic projection apparatus according to claim 1, wherein thetemperature controller comprises a liquid flow rate adjustment deviceconfigured to adjust a flow rate of the liquid so as to optimize adifference between the substantially common target temperature and thetemperatures of the substrate, the liquid and the at least part of theprojection system.
 3. The lithographic projection apparatus according toclaim 1, wherein the temperature controller comprises a liquidtemperature adjustment device configured to adjust the liquidtemperature so as to optimize a difference between the substantiallycommon target temperature and the temperatures of the substrate, theliquid and the at least part of the projection system.
 4. Thelithographic projection apparatus according to claim 1, wherein thetemperature controller comprises a PID controller configured to achieveconvergence towards the substantially common target temperature.
 5. Thelithographic projection apparatus according to claim 1, wherein thesubstantially common target temperature is set to a predetermined value.6. A lithographic apparatus comprising: an illumination systemconfigured to condition a radiation beam; a support constructed to holda patterning device, the patterning device being capable of impartingthe radiation beam with a pattern in its cross-section to form apatterned radiation beam; a substrate table constructed to hold asubstrate; a projection system configured to project the patternedradiation beam onto a target portion of the substrate; a liquid supplysystem configured to at least partly fill a space between the projectionsystem and the substrate with a liquid; and a projection systemcompensator configured to adjust an optical property of the projectionsystem in response to a distortion in a pattern exposed on the substratecaused by a difference in temperature of the projection system, thesubstrate, the liquid, or any combination thereof, from a targettemperature.
 7. The lithographic apparatus according to claim 6, whereinthe projection system compensator comprises a patterned radiation beamdistortion detector arranged to detect distortion of the patternedradiation beam.
 8. The lithographic apparatus according to claim 7,wherein the patterned radiation beam distortion detector comprises: anoptical detector arranged to detect radiation of the patterned radiationbeam reflected from the substrate; and a comparator configured tocompare the detected radiation with a standard pattern in order todetect a distortion of the patterned radiation beam.
 9. The lithographicapparatus according to claim 6, wherein the projection systemcompensator comprises: a temperature sensor arranged to measure thetemperature of at least a part of the projection system, the substrate,the liquid, or any combination thereof; and a storage device capable ofstoring a table of calibration data, the calibration data representingadjustments to be applied to an optical property of the projectionsystem in response to a measurement of the temperature sensor.
 10. Thelithographic projection apparatus according to claim 6, wherein theprojection system compensator comprises a PID controller configured toachieve convergence of the distortion to within a limit.
 11. A devicemanufacturing method comprising: projecting, using a projection systemof a lithographic apparatus, a patterned beam of radiation through aliquid onto a target portion of a substrate; and adjusting thetemperature of the substrate, the liquid and at least a part of theprojection system towards a substantially common target temperature. 12.The method according to claim 11, wherein adjusting the temperaturecomprises adjusting a flow rate of the liquid so as to optimize adifference between the substantially common target temperature and thetemperatures of the substrate, the liquid and the at least part of theprojection system.
 13. The method according to claim 11, whereinadjusting the temperature comprises adjusting the liquid temperature soas to optimize a difference between the substantially common targettemperature and the temperatures of the substrate, the liquid and the atleast part of the projection system.
 14. The method according to claim11, wherein adjusting the temperature is performed using a PIDcontroller to achieve convergence towards the substantially commontarget temperature.
 15. The method according to claim 11, wherein thesubstantially common target temperature is set to a predetermined value.